If the above code is found in your header template, you will need to change the modification.
Find:
Code:
vB_Template::preRegister('navbar',array('soundnotification' => $soundnotification));
Replace:
Code:
vB_Template::preRegister('header',array('soundnotification' => $soundnotification));
I really dislike the way 4.0 does vars... Makes things more difficult. I'll fix this in the new version.